This invention is related to electromagnetic flow meters, and more specifically, relates to a replacement transducer for known transducers used in extracorporeal measurement of blood flow or other conductive liquids.
The use of electromagnetic flow meters to measure fluid flow of conductive fluids, such as blood, is well known. A basic concept, for example, is described in U.S. Pat. No. 2,149,847. By passing blood, either in a tube or blood vessel oriented at right angles to a magnetic field, an electromagnetic field, EMF, is produced at right angles to the magnetic field and at right angles to the direction of blood flow, since the blood has the property of a moving conductor cutting through the magnetic field. The voltage generated is proportional to the velocity of flow and therefore directly proportional to the volume rate of flow of the fluid. The voltage can be measured by electrodes placed at diametrically opposite points of the tube along a diameter extending perpendicular to the magnetic lines of the flux.
Because the electrodes, magnet structure, and fluid passage must be maintained in a fixed predetermined relationship in order to maintain accurate calibration of the flow measurement, it has been the practice heretofore to assemble the tube, electrodes, and magnet structure as a unit and direct flow of blood or other conductive fluids through the tubular section in making measurements. It has been my observation that such unitary structure has several disadvantages in extracorporeal use. First, it is difficult to sterilize effectively after use. Also different size units must be provided to accommodate measurements in different size flow lines. Where measurements are to be taken at more than one point in the extracorporeal circuit, a plurality of separate complete flow meter units are required.
My In Line Electromagnetic How Measurement Transducer described in U.S. Pat. No. 4,195,515 improved on prior art electromagnetic measuring units by making the unit into separable parts that can be readily assembled and disassembled. One part includes a tube with electrode sensors that can be disposed of, or readily and easily changed and sterilized by conventional techniques. The other part included a magnet structure for generating the required magnetic field, and quick disconnect electrical connections for the electrodes of the tube. The magnetic structure can be used with different size tubular units so that measurements can be made at different points in a extracorporeal circuit wherein different size tubular units are positioned at said different points. The magnetic structure is simply moved from one tubular unit to another.
The magnetic structure in my '515 device is comprised of a C-shaped magnetic core, a coil winding on the core and at least three female connection terminals for connection to at least three male terminals formed from the electrodes of the tubular unit.
The Blood How Detection Device described by Donald K. Georgi, et al. in U.S. Pat. No. 4,881,413 (hereafter; Bioprobe) is comprised of a reusable transducer unit having six connectors separately positioned to provide three connectors on each diametrically opposite side of a tubular unit inserted therein. The transducer unit comprises a single "C" shaped magnet for producing a magnetic field through which the blood flows. The tubular unit has six electrodes with three electrodes on diametrically opposite sides of the tube and the bore of the tube is narrower in the central section thereof as compared to the end sections. I have noticed that this arrangement of electrodes results in a cumbersome assembly when connecting the tubular unit to the transducer unit. The six electrodes of the disposable tubular units are in contact with the conductive fluid as the fluid flows through the tube. The increased number of electrodes concomitantly increases the surface area of the electrodes in contact with the flowing fluid, thereby causing decreased stability during the measuring process.